Pollution Data and Contents

Air pollution information is also used as a guide for prescribed burning and for issuing burning permits. Each day the data released will be as follows:

Morning 500 meter mixing height temperature and transport wind
Afternoon mixing height and transport wind

Ventilation Index...which is the product of the afternoon Transport Wind (Meters/Second) and Mixing Height (Meters).

Category Day: Guideline for Prescribed Burning in Arkansas and Louisiana in Metric Units

1. A Category Day of ONE...which is No Burning. It has a ventilation rate of less then 2000.
2. A Category Day of TWO...which is No Burning after 11:00 am and not until surface inversion has lifted. It has a ventilation rate of 2000 to 4000.
3. A Category Day of THREE...Daytime Burning only, but not before surface inversion has lifted. It has a ventilation rate of 4000 to 8000.
4. A Category Day of FOUR...Burning anytime. For Night Burns use backing fire with surface wind speeds greater than 4 mph. It has a ventilation rate of 8000 to 16,000.
5. A Category Day of FIVE...Unstable and Windy. Excellent smoke dispersal. Burn with Caution. It has a ventilation rate of greater than 16,000.

Estimating the Stability Class of the atmosphere out of Arkansas.

• A is very Unstable(Excellent dispersion and Windy)
• B is Unstable
• C is Slightly Unstable
• D is Neutral
• E is Slightly Stable
• F is Stable(Strong Inversion in place...Capped)

The Stability Class used in Fire Weather forecasts is based on wind, incoming solar radiation, and cloud cover. The wind speed is the average wind expected for the period of concern, either daytime or nighttime.

Calculations are being made from the ETA NWS Weather Model and will be compared to AWIPS model soundings as well as area soundings for comparison purposes. Temperature and transport wind information is calculated for each forecast zone in the County Warning Area. During the comparison, quality control adjustments will be made to the mixing heights and transport wind, to ensure as much accuracy as possible.

Mixing heights are in feet/meters and transport winds in meters/second and mph. These are calculated values from a standard plot of the vertical temperature, moisture, and wind profiles. The mixing height defined as that height above ground level to which a parcel of air will rise using dry adiabatic thermal bouyancy. The transport wind is the average windspeed through the mixing layer and average direction...using eight points of a compass.

The Mississippi Forestry Commission only issues burning permits when the mixing height is at least 500 meters and the transport wind is at least 3.5 m/s.

The Louisiana and Arkansas Forestry Agencies are similar and will only issue permits if the mixing height is at least 500 meters or 1700 feet with a transport wind of 4 meter/sec or 7 mph.

The remarks section will explain the nature of the wind shift and its significant affects on Forestry Operations.